Fischer-tropsch derived diesel fuel and process for making same

ABSTRACT

The present invention is directed to a Fischer-Tropsch derived distillate suitable for use as a distillate fuel having a flash point 38° C. minimum measured by ASTM D 93 and a cloud point of +14° C. or less and further containing not less than 0.01 wt,% oxygen in each of 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol and not more than 0.01 wt.% oxygen in C 11+  linear alcohols. Preferably, the Fischer-Tropsch derived distillate will have a cloud point at or below 0° C., and more preferably the cloud point of the Fischer-Tropsch derived distillate, will be at or below −15° C.

FIELD OF THE INVENTION

The invention relates to a Fischer-Tropsch diesel fuel, distillate fuel,or blend component, which also meets the specifications for diesel fuelbut with a lighter density than conventional diesel fuel and a processfor preparing the fuel.

BACKGROUND OF THE INVENTION

A distillate fuel refers to a fuel containing components boiling abovethe typical end point of gasoline (approximately 400° F. or 204° C.),but excludes non-distillable components (material boiling above 1100° F.or 593° C.). Distillate fuels can be burned in stationary engines, suchas those used to generate electricity. A diesel fuel refers to adistillate which may be burned in a diesel engine to provide power forvarious human activities. The specifications for diesel fuel are morestringent than distillate fuels. For example in the United States, theend point specification for diesel fuels are 640° F. (338° C.) for No.2-D and 550° F. (288° C.) for No. 1-D.

Various grades of diesel fuel have specifications which place limits onthe cloud point. These frequently vary by geographical region and timeof year. For example, ASTM D975-00 defines the specifications for No.1-D and No. 2-D diesel fuels in the United States. It includes thestatement in footnote j of Table 1, “Tenth percentile minimum airtemperatures for U.S. locations are provided in Appendix X4 as a meansof estimating expected regional temperatures. This guidance is general.Some equipment designs or operations may allow higher or require lowercloud point fuels.” The temperatures in Appendix X4 range from a low of−49° C. for the northern region of Alaska in January, to +14° C. forsouthern Florida in October. Likewise the World Wide Fuel Charter (2002)includes the statement that the cloud point “maximum must be equal to orlower than the lowest expected ambient temperature.” Thus acceptablediesel fuels should have cloud points at or below +14° C., for example,at or below 0° C., or at or below −15° C., or at or below −25° C., or ator below −49° C. Because their composition will be highly paraffinic,their densities may be below specifications. Where the specificationdensity of conventional diesel fuel needs to be maintained, thesecompositions of the invention are best used as blend stocks.

The Fischer-Tropsch process provides a way to convert a variety ofhydrocarbonaceous resources into products usually provided by petroleum.These include diesel fuel. In preparing hydrocarbons via theFischer-Tropsch process, a hydrocarbonaceous resource, such as, forexample, natural gas, coal, refinery fuel gas, tar sands, oil shale,municipal waste, agricultural waste, forestry waste, wood, shale oil,bitumen, crude oil, and fractions from crude oil, is first convertedinto synthesis gas which is a mixture comprising carbon monoxide andhydrogen.

Synthesis gas generation process is one that converts ahydrocarbonaceous asset into synthesis gas by use of a gaseous oxidant.The gaseous oxidant can be purified O₂, enriched air, air, steam, carbondioxide and combinations. The process can either be above ground orin-situ. Examples of above ground synthesis gas generation processesthat use gaseous hydrocarbons having carbons numbers less than 20 (forexample methane) as feedstocks for the reactor are AutoThermal Reformer(ATR), Partial Oxidation (POX), Gas Heater Reformer (GHR), and steamreforming. When these feedstocks contain more than 2 mol % C₂ andheavier hydrocarbons, a pre-converter (pre-reformer) is often used toconvert the C₂+ hydrocarbons into methane. The pre-reformer uses acatalyst containing a Group VIII metal catalyst (for example Ni) withhydrogen at super-atmospheric pressures. An example of synthesis gasproduction is described in Kirk Othmer On-Line Edition “Fuels,Synthetic, Liquid Fuels” especially section 1, pages 2 to 14 onlineEdition incorporated herein by reference.

And in the same on-line reference “Methanol 4. Manufacture andProcessing” at pages 299 to 311, incorporated herein by reference.

Synthesis gas can also be generated by reacting undergroundhydrocarbonaceous assets with a gaseous oxidant. An example of thisin-situ process is described in

U.S. Pat. No. 6,698,515, issued Mar. 2, 2004 to Karanikas et al.Examples of underground hydrocarbonaceous assets are coal, oil shale,heavy oil, tar sands, petroleum deposits and bitumen. An example of apetroleum deposit suitable for in-situ conversion is a petroleum depositfrom which the easily-extractable petroleum has been extracted byconventional methods such as pumping, steam flooding, and waterflooding.

The synthesis gas, in turn, is converted into synthetichydrocarbonaceous compounds that have a predominantly linear structure,primarily n-paraffins, 1-alcohols, 1-olefins, and traces of otherspecies. These hydrocarbonaceous species may be refined into variousproducts, including distillate fuels.

European Patent Nos. 0861311, 0885275; U.S. Pat. Nos. 5,689,031,6,274,029, 6,296,757, 6,607,568, 6,822,131 describe the preparation of aFischer-Tropsch derived product containing C₅-C₂₄ primary linearalcohols and preferably primary linear alcohols C₁₂-C₂₄ or C₁₂₊ primarylinear alcohols. Exactly what primary linear alcohols are supposed toencompass is unclear. However, these middle distillates have a densityless than diesel fuel specification. The presence of alcohols areclaimed to improve the lubricity of the middle distillate fuel.Unfortunately, the compositions taught in these documents employing therange of alcohols specified, particularly with C₁₁ plus alcohols, wouldfail to meet the cloud point specifications for diesel fuel, and,consequently, they would not be suitable as commercial diesel fuel. Thepresent invention comes from the realization that the alcohols must beC₁₀ and lower and is particularly directed to Fischer-Tropsch deriveddiesel fuel compositions which are able to meet the cloud point,preferably, enhancing yields in the process.

Cloud point represents the temperature below which solid hydrocarbonsmay form in diesel fuels. Cloud point is determined by ASTM D 2500 whichmeasures the fuel temperature at which solid hydrocarbon crystals formedon cooling.

As used in this disclosure the phrase “Fischer-Tropsch derived” refersto a hydrocarbon stream in which a substantial portion, except for addedhydrogen, is derived from a Fischer-Tropsch process regardless ofsubsequent processing steps, and regardless of the methods of making thesynthesis gas. The feed for the creation of the “Fischer Tropschderived” refers to products derived from any carbon source, for examplenatural gas, coal, refinery fuel gas, tar sands, oil shale, municipalwaste, agricultural waste, forestry waste, wood, shale oil, bitumen,crude oil, and fractions from crude oil.

As used in this disclosure the word “comprises” or “comprising” isintended as an open-ended transition meaning the inclusion of the namedelements, but not necessarily excluding other unnamed elements. Thephrase “consists essentially of” or “consisting essentially of” isintended to mean the exclusion of other elements of any essentialsignificance to the composition. The phrase “consisting of” or “consistsof” are intended as a transition meaning the exclusion of all but therecited elements with the exception of only minor traces of impurities.

SUMMARY OF THE INVENTION

The present invention is directed to a Fischer-Tropsch deriveddistillate suitable for use as a diesel fuel having a flash point of 38°C. minimum measured by ASTM D 93 and a cloud point of +14° C. or lessand further containing not less than 0.01 wt. % oxygen in at least two1-alcohols of 1-pentanol, 1-hexanol. 1-heptanol, 1-octanol, 1-nonanol,and 1-decanol and not more than 0.01 wt. % oxygen in C₁₁₊ linearalcohols. Mixtures of all the C₅-C₁₀ alcohols are within the scope ofthe invention. The upper wt. % oxygen limit of the alcohols is less thanan amount which has the fuel failing the appropriate cloud point and/orother fuel specifications. Optionally two of the three alcohols can beused in a concentration not less than 0.03 wt. % oxygen for the twospecies, i.e., C₅ and C₇ or C₅ and C₆ or C₆ and C₇. The Fischer-Tropschderived distillate fuel will have a cloud point of +14° C. or less, forexample, at or below 0° C., or at or below −15° C., or at or below −25°C., or at or below −49° C. All the wt. % oxygen amounts are on a waterfree basis. Where density forms part of the diesel fuel specification,Fischer-Tropsche diesels will contain supplements to reach theappropriate density specification.

It is useful to summarize the boiling points of various paraffins andalcohols:

Boiling Boiling Melting Melting Point of Point of Point of Point of then- the 1- the n- the 1- Carbon Paraffin Alcohol Paraffin Alcohol Number(° F., ° C.) (° F., ° C.) (° F., ° C.) (° F., ° C.) 5 97, 36 281, 138−201, −130 −110, −79  8 258, 125 381, 193 −71, −56  +2, −17 10 346, 174441, 227 −23, −30 +45, +7  11 384, 195 469, 242 −14, −25 +61, +16 12422, 216 495, 257 +14, −10 +79, +26 14 489, 254 545, 285 +42, +6  +103,39 

To achieve a flash point by ASTM D 93 of 38° C. requires that theboiling point be 250° F. (121° C.) or higher. Because of the differentboiling points of the paraffins and alcohols, this corresponds to n-C₈and 1-pentanol. Likewise if C₁₁₊ alcohols are to be excluded, by use ofdistillation, and they boil at or above 495° F. (257° C.), then thiscorresponds to paraffins boiling at above n-C₁₄ eg, C₁₅₊ products. The640° F. (338° C.) end point of No. 2-D diesel fuel is met when theparaffins are less than or equal to C₂₀. Some branched paraffins up toC₂₄ can be included. The 550° F. (288° C.) end point of No. 1-D dieselfuel is met when the paraffins are less than or equal to C₁₆, althoughsome branched paraffins up to C₁₈ can be included. When alcohols areadded from a source other than the FT reation stream products, the cutpoint can be higher because the deleterious higher alcohols are notpresent.

The present invention is also directed to a process for preparing aFischer-Tropsch derived distillate fuel preferably maximizing yield bypermitting the C₁₅₊ products to be upgraded and retaining the C¹⁴⁻products with alcohols in the lighter fraction. The process comprises(a) separating a Fischer-Tropsch condensate into a first and secondfraction, wherein (i) said first fraction comprises not less than 0.01wt. % oxygen from at least two of 1-pentanol, 1-hexanol, 1-heptanol,1-octanol, 1-nonanol, and 1-decanol and not more than 0.01 wt. % oxygenin C₁₁₊ linear alcohols and (ii) said second fraction comprises C₁₁₊linear alcohols; (b) removing the C₁₁₊ linear alcohols from at least aportion of said heavy third fraction and recovering a treated heavyfraction substantially free of C₁₁₊ linear alcohols; and (c) blending atleast a portion of the first fraction of step a(i) and a portion of thetreated heavy fraction of step (b) in the proper proportion to prepare aFischer-Tropsch derived distillate fuel wherein the sum of the oxygenatecontent of the C₅-C₁₀ alcohols present are within the range of from 0.01wt. % oxygen and 1 wt. % oxygen, the cloud point is not more than +14°C. and the flash point of 38° C. minimum measured by ASTM D 93. Thisflash point can generally be met where 121° C. (250° F.) is the minimum5% point measured by ASTM D 2887. In carrying out the process of theinvention a third fraction may be separated from the Fischer-Tropschcondensate in step (a) which contains C⁴⁻ linear alcohols.

The present invention resides in the discovery that the presence of morethan 0.01 wt. % oxygen in C₁₁₊ linear alcohols will significantlyincrease the cloud point of the composition rendering it unsuitable foruse as a diesel fuel. Further processing the C₁₅₊ fraction also canincrease the yields since C¹⁴⁻ paraffins are suitable for use in dieselfuel. As used in this disclosure, the term “C⁴⁻ linear alcohols” refersto linear alcohols containing 4 or less carbon atoms in the molecule,such as methanol, ethanol. 1-butanol, and 1-propanol. The term “C₁₁₊linear alcohols” refers to linear alcohols having 11 or more carbonatoms in the molecule, such as 1-undecanol, 1-dodecanol. 1-tridecanol,1-tetradecanol, 1-pentadecanol, 1-hexadecanol, etc. Linear C₅-C₁₀alcohols referred to in this disclosure are 1-pentanol, 1-hexanol.1-heptanol, 1-octanol, 1-nonanol, and 1-decanol, and mixtures of these.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based upon the discovery that the presence ofas little as 0.01 wt. % oxygen in C₁₁₊ linear alcohols in aFischer-Tropsch derived distillate fuel will raise the cloud point to anunacceptable temperature. Surprisingly, the presence of C₅-C₁₀ linear1-alcohols, more specifically 1-pentanol, 1-hexanol, 1-heptanol.1-octanol, 1-nonanol, and l-decanol in the same fuel has a negligibleeffect on cloud point. Minor other alcohols species and higher carbonnumber alcohols can be included so long as the diesel fuel cloud pointspecifications are met. This generally means other alcohol species wouldbe present only as impurities. Additionally the problem to be solved wasto reduce the cost of preparation of diesel fuel by reducing theseverity of the hydrotreating operation which increases yield whilemeeting the cloud point requirements for diesel fuel.

In the process of the invention the Fischer-Tropsch product (condensate,wax or blends) is separated into at least two fractions, a firstfraction comprising C₁₀ and lower alcohols and a heavier fraction.Preferably the lighter fraction has not less than 0.01 wt. % oxygen ofat least two of 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol,and 1-decanol and not more than 0.01 wt. % oxygen in C₁₁₊ linearalcohols and a second heavier fraction comprising C₁₁₊ linear alcohols.A portion of the heavier second fraction which is intended to be blendedback into the first fraction is treated to remove substantially all ofthe C₁₁₊ linear alcohols present. Finally, the treated heavy secondfraction is blended with at least a portion of the first fraction in aproportion calculated to yield a Fischer-Tropsch derived distillate fuelhaving a cloud point of not less than +14° C. In general, the sum of theoxygenate content of the C₅-C₁₀ alcohols present the Fischer-Tropschderived distillate fuel will fall within the range of from 0.01 wt. %oxygen and 1 wt. % oxygen. Combinations of any two alcohols, i.e. C₅ andC₆ or C₅ and C₇ or C₆ and C₇ can be present in an amount from 0.01 wt. %oxygen, preferably 0.03 wt. % oxygen up to 1.0 wt. % oxygen. The fuelpreferably should also have a flash point 38° C. minimum measured byASTM D 93. Unless blended with conventional petroleum feedstocks, thedensity will be less than the standards but still function effectivelyas a distillate and diesel fuel.

The products recovered from the Fischer-Tropsch operation (condensate,wax and blends) will contain varying amounts of oxygenates. The majorityof the oxygenates present are in the form of alcohols; however, lesseramounts of ketones, aldehydes, carboxylic acids, and anhydrides may alsobe present. In order to prepare the heavy fraction which issubstantially free of C₁₁₊ linear alcohols, it is necessary to eitherremove the C₁₁₊ linear alcohols or convert them into other hydrocarbons.There are a number of processes known to those skilled in the art whichmay be used to accomplish this step. These processes include, but arenot necessarily limited to, hydrotreating, hydrocracking,hydroisomerization, dehydration, adsorption, absorption, or variouscombinations of these processes. As used in this disclosure,“substantially free of C₁₁₊ linear alcohols” means that the distillatefraction contains C₁₁₊ alcohols in an amount less than a concentrationwhich increases the cloud point to values warmer than the diesel fuelsspecification.

Hydrocracking and hydrotreating are similar processes which differprimarily in the degree of severity. They may be referred tocollectively in this disclosure as “hydroprocessing”. In the process ofthe present invention hydrocracking and hydrotreating are intendedprimarily for the purpose of removing alcohols that are present in theFischer-Tropsch distillate. “Hydrotreating” refers to a catalyticprocess, usually carried out in the presence of free hydrogen, in whichthe primary purpose when used to process conventional petroleum derivedfeed stocks is the removal of various metal contaminants, such asarsenic; heteroatoms, such as sulfur and nitrogen; and aromatics fromthe feed stock. In the present process, the primary purpose is to removethe alcohols and secondarily to saturate the olefins present. Generally,in hydrotreating operations cracking of the hydrocarbon molecules, i.e.,breaking the larger hydrocarbon molecules into smaller hydrocarbonmolecules is minimized. For the purpose of this discussion the termhydrotreating refers to a hydroprocessing operation in which theconversion is 20% or less. Conversion can be defined on the basis of theincrease in the amount of material in the product relative to the feed,boiling below the 5% point of the feed as measured by ASTM D 2887.“Hydrocracking” refers to a catalytic process, usually earned out in thepresence of free hydrogen, in which the cracking of the largerhydrocarbon molecules is a primary purpose of the operation. In contrastto hydrotreating, the conversion rate for hydrocracking, for the purposeof this disclosure shall be more than 20%. In the present invention,hydrocracking is used to remove the alcohols and to hydrogenate theolefin.

Catalysts used in carrying out hydrotreating and hydrocrackingoperations are well known in the art. See for example U.S. Pat. Nos.4,347,121 and 4,810,357, the contents of which are hereby incorporatedby reference in their entirety, for general descriptions ofhydrotreating, hydrocracking, and of typical catalysts used in each ofthe processes. Suitable catalysts include noble metals from Group VIIIA(according to the 1975 rules of the International Union of Pure andApplied Chemistry), such as platinum or palladium on an alumina orsiliceous matrix, and unsulfided Group VIIIA and Group VIB, such asnickel-molybdenum or nickel-tin on an alumina or siliceous matrix. U.S.Pat. No. 3,852,207 describes a suitable noble metal catalyst and mildconditions. Other suitable catalysts are described, for example, in U.S.Pat. Nos. 4,157,294 and 3,904,513. The non-noble hydrogenation metals,such as nickel-molybdenum, are usually present in the final catalystcomposition as oxides, or more preferably or possibly, as sulfides whensuch compounds are readily formed from the particular metal involved.Preferred non-noble metal catalyst compositions contain in excess of 5wt. % oxygen, preferably 5 to 40 wt. % oxygen molybdenum and/ortungsten, and at least 0.5, and generally 1 to 15 wt. % oxygen of nickeland/or cobalt determined as the corresponding oxides. Catalystscontaining noble metals, such as platinum, contain in excess of 0.01%metal, preferably between 0.1 and 1.0% metal. Combinations of noblemetals may also be used, such as mixtures of platinum and palladium.

The hydrogenation components can be incorporated into the overallcatalyst composition by any one of numerous procedures. Thehydrogenation components can be added to matrix component by co-mulling,impregnation, or ion exchange and the Group VI components, i.e.;molybdenum and tungsten can be combined with the refractory oxide byimpregnation, co-mulling or co-precipitation. Although these componentscan be combined with the catalyst matrix as the sulfides, that isgenerally not preferred, as the sulfur compounds can interfere with theFischer-Tropsch catalysts.

The matrix component can be of many types including some that haveacidic catalytic activity. Ones that have activity include amorphoussilica-alumina or may be a zeolitic or non-zeolitic crystallinemolecular sieve. Examples of suitable matrix molecular sieves includezeolite Y, zeolite X and the so called ultra stable zeolite Y and highstructural silica:alumina ratio zeolite Y such as that described in U.S.Pat. Nos. 4,401,556; 4,820,402; and 5,059,567. Small crystal sizezeolite Y, such as that described in U.S. Pat. No. 5,073,530 can also beused. Non-zeolitic molecular sieves which can be used include, forexample, silicoaluminophosphates (SAPO), ferroaluminophosphate, titaniumaluminophosphate and the various ELAPO molecular sieves described inU.S. Pat. No. 4,913,799 and the references cited therein. Detailsregarding the preparation of various non-zeolite molecular sieves can befound in U.S. Pat. Nos. 5,114,563 (SAPO) and 4,913,799 and the variousreferences cited in U.S. Pat. No. 4,913,799. Mesoporous molecular sievescan also be used, for example the M41S family of materials as describedin J. Am. Chem. Soc. 114:10834-10843(1992)), MCM-41; U.S. Pat. Nos.5,246,689: 5,198,203; and 5,334,368; and MCM-48 (Kresge et al., Nature359:710 (1992)). Suitable matrix materials may also include synthetic ornatural substances as well as inorganic materials such as clay, silicaand/or metal oxides such as silica-alumina, silica-magnesia,silica-zirconia, silica-thoria, silica-berylia, silica-titania as wellas ternary compositions, such as silica-alumina-thoria,silica-alumina-zirconia, silica-alumina-magnesia, and silica-magnesiazirconia. The latter may be either naturally occurring or in the form ofgelatinous precipitates or gels including mixtures of silica and metaloxides. Naturally occurring clays which can be composited with thecatalyst include those of the montmorillonite and kaolin families. Theseclays can be used in the raw state as originally mined or initiallysubjected to calumniation, acid treatment or chemical modification.

In performing the hydrocracking and/or hydrotreating operation, morethan one catalyst type may be used in the reactor. The differentcatalyst types can be separated into layers or mixed.

Hydrocracking conditions have been well documented in the literature. Ingeneral, the overall LHSV is 0.1 hr-1 to 15.0 hr-1 (v/v), preferablyfrom 0.25 hr-1 to 2.5 hr-1. The reaction pressure generally ranges from500 psig to 3500 psig (10.4 MPa to 24.2 MPa, preferably from 1500 psigto 5000 psig (3.5 MPa to 34.5 MPa). Hydrogen consumption is typicallyfrom 500 to 2500 SCF per barrel of feed (89.1 to 445 m3 H2/m3 feed).Temperatures in the reactor will range from 400° F. to 950° F. (205° C.to 510° C.), preferably ranging from 650° F. to 850° F. (340° C. to 455°C.).

Typical hydrotreating conditions vary over a wide range. In general, theoverall LHSV is 0.5 to 5.0. The total pressure ranging from 200 psig to2000 psig. Hydrogen recirculation rates are typically greater than 50SCF/Rbl, and are preferably between 1000 and 5000 SCF/Bbl. Temperaturesin the reactor will range from 400° F. to 800° F. (205° C. to 425° C.).

“Hydroisomerization”, also called simply “isomerization”, is intended toimprove the cold flow properties of the Fischer-Tropsch derived productby the selective addition of branching into the molecular structure. Inthe present invention, it may also be used to remove the alcohols.Isomerization ideally will achieve high conversion levels of the normalparaffins to iso-paraffins while at the same time minimizing theconversion by cracking. Isomerization operations suitable for use withthe present invention typically uses a catalyst comprising an acidiccomponent and may optionally contain an active metal component havinghydrogenation activity. The acidic component of the catalysts preferablyincludes an intermediate pore SAPO, such as SAPO-11, SAPO-31, andSAPO-41, with SAPO-11 being particularly preferred. Intermediate porezeolites, such as ZSM-22, ZSM-23, SSZ-32, ZSM-35, and ZSM-48, also maybe used in carrying out the isomerization. Typical active metals includemolybdenum, nickel, vanadium, cobalt, tungsten, zinc, platinum, andpalladium. The metals platinum and palladium are especially preferred asthe active metals, with platinum most commonly used.

The phrase “intermediate pore size”, when used herein, refers to aneffective pore aperture in the range of from 4.0 to 7.1 Angstrom whenthe porous inorganic oxide is in the calcined form. Molecular sieveshaving pore apertures in this range tend to have unique molecularsieving characteristics. Unlike small pore zeolites such as erionite andchabazite, they will allow hydrocarbons having some branching into themolecular sieve void spaces. Unlike larger pore zeolites such asfaujasites and mordenites, they are able to differentiate betweenn-alkanes and slightly branched alkenes, and larger alkanes having, forexample, quaternary carbon atoms. See U.S. Pat. No. 5,413,695. The term“SAPO” refers to a silicoaluminophosphate molecular sieve such asdescribed in U.S. Pat. Nos. 4,440,871 and 5,208.005.

In preparing those catalysts containing a non-zeolitic molecular sieveand having an hydrogenation component, it is usually preferred thai themetal be deposited on the catalyst using a non-aqueous method.Non-zeolitic molecular sieves include tetrahedrally-coordinated [AlO2and PO2] oxide units which may optionally include silica. See U.S. Pat.No. 5,514,362. Catalysts containing non-zeolitic molecular sieves,particularly catalysts containing SAPO's, on which the metal has beendeposited using a non-aqueous method have shown greater selectivity andactivity than those catalysts which have used an aqueous method todeposit the active metal. The non-aqueous deposition of active metals onnon-zeolitic molecular sieves is taught in U.S. Pat. No. 5,939,349. Ingeneral, the process involves dissolving a compound of the active metalin anon-aqueous, non-reactive solvent and depositing it on the molecularsieve by ion exchange or impregnation.

The dehydration of alcohols may be accomplished by processing thefeedstock over a catalyst, such as gamma alumina. During dehydration thealcohols are converted into olefins. The dehydration of alcohols toolefins is discussed in Chapter 5, “Dehydration” in Catalytic Processesand Proven Catalysis by Charles L. Thomas, Academic Press, 1970. Anotherprocess is disclosed and completely incorporated herein by reference inU.S. Pat. No. 6,933,323.

Another method, also described in examples of U.S. Pat. No. 6,933,323,for removing the alcohols involves passing the condensate through anadsorption bed containing an adsorbent capable of adsorbing thealcohols. A satisfactory adsorbent may include a molecular sieve havinglow silica to alumina ratio. Large pore molecular sieves having a lowsilica to alumina ratio, particularly those molecular sievescharacterized as having an FAU type of framework, are generally suitablefor use as an adsorbent for alcohols and other oxygenates. Preferred FAUmolecular sieves are X zeolites, with 13X zeolite being particularlypreferred. As used herein, the term “FAU molecular sieve” refers to theIZA Structure Commission standard which includes both X and Y zeolites.

The synthesis of X-type zeolites is described in U.S. Pat. Nos.2,882,244; 3,685,963; 5,370,879; 3,789,107 and 4,007,253 which arehereby incorporated herein by reference in their entirely. 13X Zeoliteare a faujasite (FAU) type X zeolite. It has a low silica/alumina ratioand is comprised of silicon, aluminum and oxygen. The oxygen ringprovides a cavity opening of 7.4 angstroms, but can adsorb molecules upto 10 angstroms. 13X zeolite have a Chemical Abstracts (CAS) number of[63231-69-6]. 13X zeolite are commercially available from severalsources, including Aldrich Chemical Company and the Davison Division ofW. R. Grace. Additionally the process as described in U.S. Pat. No.6,933,323 can be used herein as noted above.

Flash point is the temperature to which the fuel must be heated tocreate sufficient fuel vapor above the surface of the liquid fuel forignition to occur when exposed to an open flame. Flash point determinedby ASTM D 93 and preferably is a minimum of 38° C.

The following examples highlight the problem to be solved by therealization of the effect of including C₁₁₊ alcohols in distillate fueland not being able to meet diesel cloud point specifications.

EXAMPLE 1

In this example, a 600° F. (315° F.) end point (by ASTM D2887) FischerTropsch diesel fuel with a high i/n ratio was prepared and tested.

A commercial sample of Fischer Tropsch C₈₀ wax was obtained from Mooreand Munger Co. It has an initial boiling point as determined by ASTM D2887 of 790° F. and a boiling point at 5 wt. % of 856° F. It washydrocracked in a single stage pilot plant at 669° F., 1.0 LHSV, 1000psig, 10000 SCF/Bbl Hydrogen at 90% conversion in a once-throughoperation (without recycle). A commercial sulfided hydrocrackingcatalyst was used. A 260-600° F. product with the following propertieswas recovered by distillation. This product contains over 2 wt. % n-C₁₄₊n-paraffins yet has a cloud point of −51° C.

Density at 15° C., g/ml 0.7626 Sulfur, ppm 0 Viscosity at −20° C., cSt6.382 Freeze Point, ° C. −47.7 Cloud Point, ° C. −51. Flash Point, ° C.54. Smoke Point, mm >45

Hydrocarbon types, wt. % by Mass Spec. (ASTM D2789)

Paraffins 93.1 Mono-cycloparaffins 5.2 Di-cycloparaffins 1.5Alkylbenzenes 0.1 Benzonaphthalenes 0.0 Naphthalenes 0.1

N-paraffin Analysis by GC CARBON DISTRIBUTION NORMAL NON NUMBER (Wt.Percent) PARAFFIN N-PARAFFIN 6 0.00 0.00 0.00 7 0.00 0.00 0.00 8 0.120.10 0.02 9 8.75 1.83 6.92 10 10.95 1.56 9.39 11 11.25 1.22 10.03 1211.24 1.19 10.05 13 11.26 0.68 10.58 14 10.66 0.77 9.90 15 10.21 0.589.62 16 9.70 0.41 9.29 17 9.37 0.30 9.07 18 6.36 0.03 6.33 19 0.12 0.000.12 20 0.02 0.00 0.02 21 0.00 0.00 0.00 22-52 0.00 0.00 0.00 TOTAL100.00 8.67 91.33 Average Carbon Number: 13.28 Average Molecular Weight:187.93

Simulated Distillation, ° F. by wt. %, ASTM D 2887

0.5%  267  5% 287 10% 310 20% 342 30% 378 40% 405 50% 439 60% 472 70%504 80% 535 90% 564 95% 579 99% 595 99.5%   598

This sample was mixed with n-dodecanol in varying amounts and the cloudpoint was determined. The original sample had a cloud point of −51° C.which meets the most stringent cloud point specification in ASTM D975,but adding as little as 0.1 wt. % oxygen as dodecanol significantlyincreased the cloud point.

Blending of Diesel Fuel with 1-Dodecanol for Cloud Point Measurements

Fischer-Tropsch Diesel Fuel Pour Test Wt Wt Diesel Fuel, Total Wt in,Actual Wt % Target Wt % Wt % Cloud Point, Point, No 1-Docecanol, g g g1-Dodecanol 1-Dodecanol Oxygen ° C. ° C. 1 0 0 0.00 −51 <−59 2 0.130910.8550 10.9859 1.19 1.18 0.10 −8 3 0.5910 49.4220 50.0130 1.18 1.180.10 −9 −38 4 0.5878 9.5348 10.1226 5.81 5.79 0.50 1 5 3.0133 49.051152.0644 5.79 5.79 0.50 3 −1

EXAMPLE 2

An additional diesel fuel sample was prepared with a 675° F. (357° C.)and 450° F. (232° C.) end points and a moderate i/n ratio and tested asshown below. This sample meets the end point and flash pointrequirements of ASTM D975 for No. 2-D fuel.

Samples of Fischer Tropsch condensate and wax from a cobalt catalystwere obtained. The condensate was hydrotreated at 3.36 LHSV, 1000 psigtotal pressure, 5000 SCFR recycle gas rate over a sulfided commercialwhole extrudate non-acidic NiMo/Al₂O₃ catalyst. The wax was hydrocrackedat 1.2 LHSV, 66% per pass conversion below 675° F. (357° C.), 1000 psigtotal pressure, 5000 SCFB recycle gas rate over a sulfided commercialwhole extrudate acidic NiW/Al₂O₃—SiO₂ catalyst. The products from thetwo units were continuously blended and distilled. The material boilingabove the diesel cut point (roughly 675° F.-357° C.) was recycled toextinction in the hydrocracker.

Properties of the 250-675° F. (121-357° C.) diesel fuel are shown below:

Gravity, °API 52.7 Nitrogen, ppm 0.24 Sulfur, ppm <1 Water, ppm by KarlFisher, ppm 21.5 Pour Point/Cloud Point/CFPP, −23/−18/−21/−14 °C./Freeze Point, ° C. Flash Point, ° C. 58 Viscosity at 25° C. × 40° C.,cSt 2.564/1.981 Cetane Number 74 Aromatics by Supercritical <1 FluidChromatography, wt % Neutralization No. 0 Ash Oxide, Wt % <0.001Ramsbottom Carbon Residue, wt % 0.02 Cu Strip Corrosion 1A Color, ASTMD1500 0 GC-MS Analysis Paraffins, Wt % 100 Paraffin i/n ratio 2.1 Oxygenas oxygenates, ppm <6 Olefins, Wt % 0 Average Carbon Number 15.15Distillation by D-2887 by Wt %, ° F. and D-86 by Vol %, ° F. D-2887 D-860.5/5 255/300 329/356 10/20 326/368 366/393 30/40 406/449 419/449 50 487480 60/70 523/562 510/539 80/90 600/637 567/597 95/99.5 659/705 615/630

Detailed GC-MS Analysis.

N-alkane Branched Total i/n by Formula area % alkane area % alkanesCarbon No. C9H20 2.96 0.00 2.96 — C10H22 3.59 4.24 7.83 1.18 C11H24 3.804.65 8.45 1.22 C12H26 3.65 4.77 8.42 1.31 C13H28 3.41 5.34 8.75 1.57C14H30 3.00 5.34 8.34 1.78 C15H32 2.61 5.56 8.17 2.13 C16H34 2.33 8.6510.98 3.71 C17H36 1.99 5.74 7.72 2.89 C18H38 1.51 6.11 7.62 4.04 C19H401.60 5.98 7.58 3.73 C20H42 1.18 5.35 6.53 4.52 C21H44 0.58 3.82 4.416.54 C22H46 0.22 2.00 2.23 8.94

This diesel fuel was mixed with various primary linear alcohols and thecloud point determined. Adding 1-heptanol makes no significant change inthe cloud point, but adding C₁₁₊ alcohols does increase the cloud point.These results show that a +14° C. cloud point cannot be achieved whenthe C₁₆₊ alcohol content is in excess of 0.3 wt % oxygen as oxygenates.Adding 1-hexanol does not make a significant increase in the cloudpoint, but adding 1-dodecanol does. When C₁₁₊ alcohols were present inblends with 1-hexanol, significant increase in the cloud point was stillobserved in most cases. High levels of 1-hexadecanol and 1-eicosanolwere not soluble at ambient conditions (and even 50° C.). Thus cloudpoints could not be measured. They were well in excess of +14° C.

Experi- Actual ment Oxygen Cloud No Alcohol Wt % Point Comments 1 None 0−18, −19; −20; −20 2 1-Hexanol 0.0010 −19 3 1-Hexanol 0.0101 −19 41-Hexanol 0.3000 −20 Soluble at ambient 5 1-Dodecanol 0.0010 −17 61-Dodecanol 0.0101 −14 7 1-Dodecanol 0.2996 −3 Soluble at ambient 81-Hexadecanol 0.0010 −19 9 1-Hexadecanol 0.0101 −10 10 1-Hexadecanol0.3000 unable to Not soluble at detect ambient 11 1-Eicosanol 0.0010 −1212 1-Eicosanol 0.0100 13 Soluble at ambient 13 1-Eicosanol 0.2999 solidNot soluble at ambient, turned solid, did not determine cloud point 14Mixed Alcohols 0.0010 −18 15 Mixed Alcohols 0.0101 −10 16 Mixed Alcohols0.3000 17 Not soluble at ambient

Mixed alcohols were an equal weight percent mixture of 1-hexanol,1-dodecanol 1-hexadecanol and 1-eicosanol.

EXAMPLE 3

The diesel product from example 2 was further distilled to obtain a250-400° F. (121-204° C.) diesel fuel fraction which simulated a No. 1-Dfuel with these properties.

Property Value Units Density @ 20° C. 0.7269 g cm⁻¹ Refractive Index @20° C. 1.4096 Molecular Weight 142 Daltons n-d-M Analysis % ParaffinicCarbon 98.42 Wt % % Naphthenic Carbon 1.52 Wt % % Aromatic Carbon 0.00Wt % Naphthenic Rings per molecule 0.03 Aromalic Rings per molecule 0.00Cloud Point −60 ° C. Sulfur 2.3 ppm weight Nitrogen 0.178 ppm weightBromine Index 228 Aromatics by SFC Monoaromatics <0.5 Wt % Polyaromatics<0.5 Wt % Total Aromatics <0.5 Wt % FIAM (D1319) Aromatics 1 Vol %Olefins 0 Vol % Paraffins/Naphthenes 99 Vol % n-Paraffin Analysis byCarbon Number n-C₅ 0.01 Wt % n-C₆ 0.01 Wt % n-C₇ 0.50 Wt % n-C₈ 11.13 Wt% n-C₉ 16.42 Wt % n-C₁₀ 16.97 Wt % n-C₁₁ 13.59 Wt % n-C₁₂ 0.46 Wt %n-C₁₃ and heavier 0.00 Wt % Total Normal Paraffins 59.09 Wt %Distilliation by D-2887, Wt % by ° F. St/5 wt % 196/256 10/30 wt %260/304 50 wt % 330 70/90 wt % 350/388 95/99 wt % 389/406

These studies show that addition of small amounts of dodecanol has asignificant detrimental impact on the cloud point. Adding as little as0.01 wt. % oxygen as 1-dodecanol resulted in cloud points (as measuredby ASTM D2500, ° C.) well in excess of the lowest cloud limit, −49° C.Adding C₅ to C₁₀ alcohols did not result in a notable increase in thecloud point. As noted above all wt. % oxygen concentrations are on awater free basis.

Preferred FT diesel alcohol compositions with 1-C₅ to 1-C₁₀ areexemplified below.

FT Diesel with 1-Heptanol

Test Wt Wt Diesel Fuel, Total wt in, Actual wt % 1- Target Wt % 1- Wt %Cloud Point, No 1-Heptanol, g g g Heptanol Heptanol Oxygen ° C. 6 0 Noadded alcohol 0 −−63 7 0.00597 8.49875 8.50472 0.07 0.0725 0.01 −61.6 80.03208 4.38771 4.41979 0.73 0.725 0.10 −58.8

FT Diesel with 1-Pentanol

Test Wt Wt Diesel Fuel, Total wt in, Actual wt % 1- Target Wt % 1- Wt %Cloud Point, No 1-Pentanol g g g Pentanol Pentanol Oxygen ° C. 9 0.003156.00633 6.00948 0.05 0.055 0.01 −61.6 10 0.03231 6.02061 6.05292 0.530.55 0.10 −55.8

FT Diesel with 1-Dodecanol

Test Wt Wt Diesel Fuel, Total wt in, Actual wt % 1- Target Wt % 1- Wt %Cloud Point, No 1-Docecanol, g g g Dodecanol Dodecanol Oxygen ° C. 110.01050 9.00597 9.01647 0.116 0.11625 0.01 −37 12 0.06792 6.001946.06986 1.119 1.1625 0.10 −11

FT Diesel with 1-Decanol

Test Wt Wt Diesel Fuel, Total wt in, Actual wt % 1- Target Wt % 1- Wt %Cloud Point, No 1-Decanol, g g g Decanol Decanol Oxygen ° C. 13 0.023323.9778 24.0011 0.10 0.09875 0.01 −52

FT Diesel with 1-Octanol

Test Wt Wt Diesel Fuel, Total wt in, Actual wt % 1- Target Wt % 1- Wt %Cloud Point, No 1-Decanol, g g g Decanol Decanol Oxygen ° C. 14 0.003314.00237 4.00568 0.083 0.08125 0.01 −60.7 15 0.08838 10.93777 11.026150.802 0.8125 0.10 −61

This examples illustrate the inability to get low cloud points withnormal alcohols such as 1-dodecanol while C₅ to C₁₀ normal alcohols canbe employed and obtain a low cloud point, especially when the distilledfraction has a lower end point than the prior example and a moderate i/nratio.

1. A Fischer-Tropsch derived distillate suitable for use as a dieselfuel having a flash point 38° C. minimum measured by ASTM D 93 a cloudpoint of +14° C. or less and further containing not less than 0.01 wt. %oxygen in at least two alcohols selected from the group consisting of1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol; andmixtures of more than two alcohols, and not more than 0.01 wt. % oxygenin C₁₁₊ linear alcohols.
 2. The Fischer-Tropsch derived distillate ofclaim 1 wherein the cloud point is 0° C.
 3. The Fischer-Tropsch deriveddistillate of claim 2 wherein the cloud point is −15° C. or less.
 4. TheFischer-Tropsch derived distillate of claim 3 wherein the cloud point is−25° C. or less.
 5. The Fischer-Tropsch derived distillate of claim 4wherein the cloud point is −49° C. or less.
 6. The Fischer-Tropschderived distillate of claim 1 wherein the sum of the oxygenate contentof the C₅-C₁₀ linear alcohols present are within the range of from 0.01wt. % oxygen and 1 wt. % oxygen.
 7. A process for preparing aFischer-Tropsch derived distillate fuel which comprises; (a) separatinga Fischer-Tropsch condensate into a first and second fraction, wherein:(i) said first fraction comprises not less than 0.01 wt. % oxygen ofalcohols selected from the group consisting of 1-pentanol, 1-hexanol,1-heptanol, 1-octanol, 1-nonanol, 1-decanol, and mixtures thereof, andnot more than 0.01 wt. % oxygen in C₁₁₊ linear alcohols and (ii) saidsecond fraction comprises C₁₁₊ linear alcohols; (b) removing the C₁₁₊linear alcohols from at least a portion of said second fraction andrecovering a treated heavy fraction substantially free of C₁₁₊ linearalcohols; and (c) blending at least a portion of the first fraction ofstep a(i) and a portion of the treated heavy fraction of step (b) in theproper proportion to prepare a Fischer-Tropsch derived distillate fuelwherein the sum of the oxygenate content of the C₅-C₁₀ alcohols presentare within the range of from 0.01 wt. % oxygen and to 1 wt. % oxygen,the cloud point is not more than +14° C., and the flash point 38° C.minimum measured by ASTM D
 93. 8. The process of claim 7 wherein thefirst fraction and the second fraction are blended in step (c) with theproper proportion to prepare a Fischer-Tropsch derived distillate fuelhaving a cloud point of not more than 0° C.
 9. The process of claim 8wherein the first fraction and the second fraction are blended in step(c) with the proper proportion to prepare a Fischer-Tropsch deriveddistillate fuel having a cloud point of not more than −15° C.
 10. Theprocess of claim 7 wherein the Fischer-Tropsch condensate is separatedinto first, second, and third fractions wherein said first and secondfractions are as described and said third fraction comprises C⁴⁻ linearalcohols.
 11. The process of claim 7 wherein the second fraction istreated by a process selected from hydrotreating, hydrocracking,hydroisomerization, dehydration, adsorption, absorption, or acombination thereof to obtain the treated heavy fraction substantiallyfree of C₁₁₊ linear alcohols.
 12. In a distillate fuel having a cloudpoint of +14° C. or less, the improvement comprising not less than 0.01wt. % oxygen in at least two alcohols selected from the group consistingof 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol,and mixtures of more than two alcohols; and not more than 0.01 wt. %oxygen in C11₊ linear alcohols.
 13. The distillate fuel of claim 12wherein the cloud point is 0° C. or less.
 14. The distillate fuel ofclaim 13 wherein the cloud point is −15° C. or less.
 15. The distillatefuel of claim 12 wherein the sum of the oxygenate content of the C₅-C₁₀linear alcohols present are within the range of from 0.01 wt. % oxygenand 1 wt. % oxygen.
 16. The diesel fuel of claim 12 wherein the alcoholis any two of the C₅-C₁₀ linear alcohols in a total concentration lessthan 1 wt. % oxygen.
 17. The Fischer-Tropsch derived distillate of claim1 wherein the alcohol is any two of the C₅-C₁₀ linear alcohols in atotal concentration less than 1 wt. % oxygen.
 18. The Fischer-Tropschderived distillate of claim 7 wherein the alcohol is any two of theC₅-C₁₀ linear alcohols in a total concentration less than 1 wt. %oxygen.
 20. The Fischer-Tropsch derived distillate according to claim 19with 1-alcohols selected from the groups consisting of C₅ and C₆; C₅ andC₇; or C₆ and C₇.
 21. The process of claim 7 wherein the first fractionfurther includes 1-alcohols C₈, C₉ and C₁₀ and step b removes the C₁₁₊linear alcohols from at least a portion of said second fraction andrecovering a treated heavy fraction substantially free of C₁₁₊ linearalcohols and step (c) blends at least a portion of the first fraction ofstep a(i) and a portion of the treated heavy fraction of step (b). 22.The diesel fuel of claim 12 further comprising 1-alcohols selected fromthe group consisting of C₈, C₉ and C₁₀ and mixtures thereof alcohols andwherein the paraffins are at least 90% i-paraffins.
 23. The diesel fuelof claim 1 further comprising 1-alcohols selected from the groupconsisting of C₈, C₉ and C₁₀ and mixtures thereof alcohols and whereinthe paraffins are at least 90% i-paraffins.